Intermittent pneumatic compression is known to be effective not only for prevention of thrombi in the deep veins after surgery but also for management of edema and circulatory complications of the veins of the leg. However, functional requirements for the two applications differ.
For the prevention of deep vein thrombi (DVT), inflation of the leg cuff should be rapid, with pressures rising to 35 or 40 millimeters Hg in 1/2 second or less. This is because thrombi are believed to originate from the pooling of stagnate blood in deep veins after trauma or surgery. Intermittent compression is thus believed to prevent thrombi formation by the mechanical flushing of the stagnate blood, and studies show that rapid inflation of a leg cuff is more effective in increasing the velocity of the blood. In commonly assigned copending U.S. application Ser. No. 08/088,895, filed Jul. 8, 1993, such a system for DVI prevention is disclosed. The system employs one or more reservoirs to accumulate air compressed to relatively high pressure during the interval between pulses. On initiation of the pulse, the cuffs inflate rapidly.
In the management of edema and venous stasis, however, such rapid inflation is unnecessary. However, it is important that the pulsating compression be applied sequentially from the distal to the proximal zones of the limb and at progressively less pressure, in order to "milk" the edema toward the heart. Systems that provide such compression are well known in the art. All such known systems achieve this sequential compression by the use of a complex multistage controller containing a separate valve and air tube for each segment of the extended cuff device. Thus, a two-segment prior art cuff would have two tubes leading from the controller to the cuff and a three-segment cuff would require three tubes leading from the controller to the cuff. Such systems are very complex and are notoriously expensive. Accordingly, these devices are often available only at a hospital or clinic that patients must visit for periodic treatment instead of having the treatment in the convenience of their home.
One such system appears to be shown in Hasty U.S. Pat. No. 4,013,069. It discloses an intermittent compression device with six compartments, divided into three adjacent pairs. Each pair is inflated at present times of t.sup.0,t.sup.1,t.sup.2 by three separate timers and shift valves. Inflation of the second compartment of each pair is through a restrictor communicating with its mating first compartment. This delays inflation of the second compartment, but its pressure ultimately rises to the same level as the first compartment. Thus these restrictors provide sequential but not graduated compression of the second compartment of each pair. All of these restrictors are located in the manifold of the controller, and each compartment of the cuff requires a separate air tube from the controller for its inflation. Thus with Hasty, six tubes are required for a six compartment cuff. All of the many sequential systems known to applicants are believed to be like this. All require a separate inflating tube for each cuff compartment. Moreover, a larger pump also is required for the larger volume of air; and, because of the structure of the cuff compartment, with no outside hard shell to restrict outward cuff expansion, there is wasted energy and efficiency.